Center adjusting device



June 5, 1962 M. D. HARE ET AL 3,037,409

CENTER ADJUSTING DEVICE Filed Dec. 23, 1959 6 Sheets-Sheet 1 INVENTORSMILTON D. HARE HECTOR A. MENESES ATTORNEYS June 5, 1962 M. D. HARE ET AL3,037,409

CENTER ADJUSTING DEVICE Filed Dec. 23, 1959 6 SheetsSheet 2 INVENTOR5MILTON D. HARE HECTOR AMENESES BY //4A04/f5 ATTORNEYJ June 5, 1962' M.D. HARE ET AL 3,037,409

CENTER ADJUSTING DEVICE Filed Dec. 2:5, 1959' 6 Sheets-Sheet s T' I 749i 8 q 8% H 2 .J g /g q- 0) 8 I: @835 g f" 1 H I g! O L8 9 8 m 3/ o g L;m 802 383 i 1a a E 5| w/ 8 8 a" 7 3 Y 3 3 i 3 I s 8 2 IE] 8 g I *2 3INVENTORS MILTON D. HARE HECTOR A. MENESES ATTORNEYS M. D. HARE ET ALCENTER ADJUSTING DEVICE June 5,' 1962 6 SheetsSheet 4 Filed Dec. 23,1959 5 5 \9m m s m 9m m x m m w ma 3m mE A 3 om DM m i 0mm N 9m 09 I momm. mm a Q. 4 4 2% MH 8 3 0S v wq 3 mm v .Y B w 7 v: on K m mm mp 0F mmom mm Q ow @m www June 5, 1962 M. D. HARE ET AL 3,037,409

CENTER ADJUSTING DEVICE Filed Dec. 23, 1959 6 Sheets-Sheet 5 llOINVENTORS MILTON D. HARE HECTOR A. MENESES BY jaw/"5M 92 94 84 ATTORNEY;

June 5, 1962 M. D. HARE ET AL 3,

CENTER ADJUSTING DEVICE Filed Dec. 25, 1959 6 heets-Sheet 6 IN VE N TORSMILTON D. HARE HECTOR A. MENESES ATTORNEYS United States Patent3,037,409 CENTER ADJUSTING DEVICE Milton D. Hare, Los Altos, and HectorA. Meneses,

Mountain View, Calif., assignors to Research Corporation, New York,N.Y., a corporation of New York Filed Dec. 23, 1959, Ser. No. 861,640 9Claims. (CI. 82-45) This invention relates to center adjusting deviceshaving particular utility on machines including a spindle adapted torotate work holding means.

There is a particular need in the industry to provide means for lathes,and boring, reaming, and honing machines and the like, wherebystructures held in work or tool holding devices may be accuratelycentered for rotation with the rotatable spindle or offset therefrom apredetermined amount. The need is particularly great where the workholding structure comprises independently movable, plural jawed chucksand Where the work piece is unsymmetrical.

It is a principal object of the present invention to provide in arotating spindle machine having a work holding member means for mountingthe work holding member for selective radial movement relative to theaxis of rotation of the spindle whereby the work may be accuratelycentered or offset a predetermined amount.

A further object is to provide such a device wherein the work holdingmeans may be rapidly and accurately adjusted relative to the axis ofrotation of the spindle of the machine.

A further object is to provide such a device that is relatively simpleas to its parts, easy to operate and which materially reduces the timerequired to center or oifset a work holding member relative to the axisof rotation of the drive spindle.

These and other objects and advantages are provided by a centeradjusting means for a machine having a rotatable spindle and a workholding member comprising means mounting the work holding member indriven relation to the spindle, said mounting means including aplurality of means having cam surfaces mounted for rotation with thespindle and selectively displaceable radially of the axis of rotation ofthe spindle, means securing the work holding member to the means havingcam surfaces, cam followers for selectively moving the means having camsurfaces radially of the axis of rotation of the spindle, and lockingmeans securing the means having cam surfaces against radial displacementrelative to the axis of rotation of the spindle.

These and other objects and advantages will be more apparent to thoseskilled in the art from the following detailed description of theinvention when considered with reference to the accompanying drawingswherein:

FIG. 1 is an elevational view of the live center or headstock end of ahollow spindle type lathe incorporating the improvements of the presentinvention;

FIG. 2 is a front elevational view of the headstock of the latheillustrated in FIG. 1 with the chuck removed to show the improvements ofthe present invention;

FIG. 3 is a vertical sectional view of the headstock of the lathe shownin FIGS. 1 and 2 substantially on line 33 of FIG. 2;

FIG. 4 is a transverse section through the headstock of the latheillustrated in FIG. 2 substantially on line 44 thereof;

FIG. 5 is an exploded view of the mounting means for the work holdingchuck of the lathe illustrated in FIGS. 1 through 4;

FIG. 6 is an enlarged fragmentary view of the mounting means permittingradial movement of the work holding chuck relative to the axis ofrotation of the spindle of the lathe;

FIG. 7 is an enlarged view of the cam surface elements embodied in theimproved adjustable mounting means of the present invention;

FIG. 8 is a diagrammatic view showing the development of the front pairof cam surfaces; and

FIG. 9 is a similar diagrammatic View showing the development of therear pair of cam surfaces.

Referring to the drawings, 10 generally designates a lathe incorporatingthe improvements of the present invention and comprises a bed portion 12and a headstock 14 slidably mounted on the bed 12. The headstock 14includes a housing which rotatably mounts a spindle 16 in conventionalbearing means 18 and 20. The spindle 16 has teeth 22 cut in a portionthereof which teeth are engaged by a timing chain which is driven by thelathe motor through suitable change speed and reverse gear means notshown in the drawings or forming part of the present invention.

A draw bar 26 is received within the 'bore 28 in the spindle of thelathe. The forward end of the draw bar 26 is provided with externalthreads 30 which threads project forwardly of the most forward edge 32of the hollow spindle 16 of the lathe. The rearward end of the draw bar26 receives an annular knob or handle 34 which knob is secured to rotatewith the draw bar. Concentrically spaced about the inner face of theannular handle 34 are a plurality of large bores 36 and a plurality ofsmall bores 38. The small bores receive threaded pins 40 with the headends of the pins passing through bores in a locking ring element 42whereby the pins 40 mount the locking ring member 42 to the annularhandle member 34 but permit relative axial movement therebetween.

Within each of the large bores 36 is a helical compression spring 44.Each of the helical draw bar compression springs 44 receives at theforward end a pin generally designated 48. Each pin has a reduceddiameter shank portion 50 and a head portion 52. The shank portion 50 ofeach pin is adapted to be slidably received in its respective helicalspring while the head portion 52 of each pin is snugly slidable in itslarge bore 36. The head portions of the pins engage face 54 of thelocking ring 42 and a ball race 56 is formed in the opposite face whichrace receives a plurality of ball bearing means 58. As clearlyillustrated in FIGS. 3 and 4 of the drawings, the ball race 56 is sopositioned that the balls 58 thereof engages end 60 of the hollowspindle 16 of the lathe.

The forward end of the spindle 16 is received in a large bore 6 2 in thelathe face plate 64. A plurality of set screws 66 threadedly received inradial bores in the face plate 64 secure the face plate to the spindlewith the base of the set screws engaging a set screw slot 70 V formed inthe forward end of the spindle 16 as more clearly shown in FIG. 4 of thedrawings whereby as the timing chain 24 rotates the spindle 16, the faceplate 64 is also rotated.

A conventional work holding chuck generally designated 76 is rotated bythe face plate 64 and the work holding chuck 76 is laterally movablerelative to the face plate 64 through the cooperative connection betweenthe following elements interposed between the face plate 64 and thechuck 76: anti-twist plate 78, cam plate member 80, draw bar nut 82 andcam plate member 84. These elements are shown in assembled relationshipin FIGS. 3, 4 and 6 and in an exploded form in FIG. 5. The chuck 76which is illustrated as a conventional four-jawed type is secured to thefront cam plate 84 by set screw means 86 which are threadably receivedin the chuck and engage a set screw groove 88 at the forward end of thecam plate 84. The cam plate 84 is provided with a cam groove generallydesignated 90 which cam groove defines an inner cam surface 92 and anouter cam surface 94. Cam surfaces 92 and 94, as will be more fullydescribed with reference to FIG. 8 are generally non-circular andeccentric to the center bore in the cam plate 34 and to each other andthe peaks thereof are radially opposed.

Cam plate 80 is also provided with a cam groove generally designated 96which cam groove defines an inner cam surface 98 and an outer camsurface 180. Cam surfaces 98 and 100 are generally non-circular andeccentric to the center bore in the cam plate and to each other and thesurfaces are closest together adjacent zone Y. The development of camsurfaces 98 and 100 will be described hereinafter with reference to FIG.9.

Cam plate 84 is rigidly secured to cam plate 80 by a plurality of bolts102 which pass through bores 194 in cam plate 84 and engage tapped bores106 in the cam plate 80. In securing cam plate 84 to cam plate 80, thepeaks of cam surfaces 92 and 94 of plate 84 and 98 and 100 of plate 80are displaced 90 from one another.

The back face of cam plate 84 and the front face of cam plate 80 arerecessed as at 108 and 110, respectively, to receive therebetween thedraw bar nut 82. As more clearly shown in FIG. 6, the diameter of thedraw bar nut 82 is less than the diameter of openings 108 and 110 in therespective cam plates and the thickness of the draw bar nut 82 is lessthan the total depth of the openings 108 and 110 in said cam plateswhereby the cam plates 80 and 84 are selectively movable with respect tothe draw bar nut as to be more fully described hereinafter.

The draw bar nut 82 is provided with internal threads 112 which matewith threads 30 on the draw bar 26. In assembled form, the nut 82 isscrewed onto the cooperating threads 30 at the forward end of the drawbar and the draw bar nut 82 is also secured to the face portion 72 ofthe face plate 64 by three screws 114 which are threadably received inthree tapped bores 116 in the face porden 72 of the face plate 64.Referring particularly to FIG. 6, it will be noted that the bores 118 inthe draw bar nut 82 for the screws 114 are larger than the screw shanksand the bores 118 each receive a bushing 120 having an axial lengthgreater than the lip 122 formed about the bore 120 by counterbore 124whereby when the screws 114 are cinched, the draw =bar nut 82 rotateswith the face plate 64 which, in turn, brings about the rotation of thedraw bar 26 and its annular handle member 34 at the rearward end of thedraw bar. The bores in the draw bar nut 82 are at least %2-IflCh largerthan the outside diameter of the bushings 128. This provides limitedradial movement therebetween to permit ease of engagement between thenut 82 and the threads on the draw bar. Through the use of the spacerbushings 120, the draw bar nut 82 also has limited axial movementrelative to the spindle 16 and the face plate 64 which movement iscontrolled through the draw bar handle 34 as to be more fully describedhereinafter.

The anti-twist plate 78 couples the rear cam plate 80 and, therefore,the front cam plate 84 and the chuck 76 to the face plate 64. As moreclearly shown in FIG. 5, the anti-twist plate 78 is provided with fourslots 121, 123, 124, and 125 which extend from the inner peripheral edge126 radially outward toward the outer peripheral surface 128 thereof.The depth of the slots 121, 123, 124, and 125 determine the amount oflateral displacement of the chuck 76 relative to the axis of rotation ofthe spindle 16, and the slots 121, 123, 124 and 125 arecircumferentially spaced 90 from each other.

The face plate 64 is provided with a pair of slots 128 and 130 displaced180 from one another and each of these slots has secured thereto, byscrews 132, slide block elements 134 and 136, respectively, as moreclearly shown in FIG. 3 of the drawings. The thickness of the slideblocks 134 and 136 is greater than the depth of the slots 128 and 130 inthe face plate 64 by an amount sub- 4. stantially equal to the thicknessof the anti-twist plate 78. These slide blocks 134 and 136 are receivedin slots 121 and 123 of the anti-twist plate and prevent relativerotative motion between the anti-twist plate 78 and the face plate 64.The back face of cam plate is similarly provided with a pair of slots138 and 140, FIGS. 4 and 5, which slots receive similar slide blocks142, one of which is illustrated in FIG. 4. The slide blocks 142 arereceived in slots 124 and of the anti-twist plate 78 and preventrelative rotative movement between the cam plate and the face plate 64.

From the foregoing description, it will be seen that as the spindle 16rotates, the chuck 76 is also rotated due to the interconnection of thecam plates 80 and 84 to the face plate 64 through the slide blockscarried by the face plate 64 and the rear cam plate 80 which cooperatewith the spaced radial slots in the anti-twist plate 78. It will also beseen that the chuck 76, the two cam plates 80 and 84 and the anti-twistplate 78 are free to slide within limits with respect to the face plate64.

Thus it will be seen that the transmission of torque or rotational driveto the chuck is through the anti-twist plate 78 and any frictionaleffects between the plate 78 and the cam plate 80 and the face plate 64are incidental as far as rotational drive for the chuck is concerned.

The headstock 14 supports a pair of plate members and 152 disposed atright angles to each other. The top plate member 150 is secured to theheadstock 14 by screw means 154 and adjacent the rearward end of theplate 150 is secured a boss 156 by screw means 158. The boss 156pivotally mounts a lever plate 160 on pivot pin 162. Adjacent theforward end of lever plate 160 is a cam follower block 164 which carriesat its lower edge a cam follower 170. The cam follower is circular inplan and rotatably mounted on the extended end of the bolt 172, securedto the block 164.

The diameter of the cam follower 170 is such that it is substantially inengagement with the inner and outer cam surfaces 98 and 100 of cam plate80 at point Y, FIG. 7, adjacent the cam peaks where the two cam surfacesare closest together. The cam lever 160 is pivoted about the pin 1.62 tomove the cam follower 170 and thus shift the relative position betweencam plate 80 and face plate 64 by rotation of the cam runout knobassembly generally designated 174.

The cam runout knob assembly 174 includes a hand knob 17 6 keyed to ashaft 178 which shaft is threadably received in a bushing 180. Thebushing 180 is received in a sleeve 182 secured in the front cam block164 and as more clearly shown in FIG. 3 of the drawings, the bushing 180is provided with a flange 184 which cooperates with a flange on thesleeve 1S2. Seated between the upper surface of the bushing 180 and anannular nut 186 threaded into the upper end of the sleeve 182 is ahelical compression spring 188. The lower end of the shaft 178, securedto the hand knob 176, abuts a hearing plate 190 inset in the upper angleplate 150. By rotating the handle 176 in one direction, the shaft 78 isscrewed toward the bearing plate 190 by cooperative engagement with theinternal threads on the bushing 180 causing the plate 160 to moveupwardly which, in turn, urges the cam follower 170 in an upwarddirection. If the hand knob 176 is rotated beyond the limits of movementof the cam plate 80 relative to the face plate 64, continued rotation ofthe knob 176 causes the bushing 188 to move the shaft 178 and its handleportion 176 upwardly against the tension in spring 188 preventing damageto the assembly.

By rotating the hand knob 176 in the opposite direction the cam leverplate 160 is moved downwardly by helical compression spring 192. Helicalcompression spring 192 is received about a post 194 threadedly mountedin a bore in angle plate 150 and in the upper surface of the headstock14. The post 194 passes through a large opening 196 in the cam leverplate 160 and the upper end of the post 194 is center bored and tappedas at 198 to receive a screw 200. The screw 200 mounts a cap piece 202to the post 194 whereby the helical spring 192 acts between the lowersurface of the cap 202 and the upper surface of the lever plate 160. Thecompressive force of the spring 192 may be adjusted by means of the capattaching screw 200.

The force applied to cam lever plate 160 by spring 192 is sufiicient tomove the chuck 76 and the cam plate 80 and 84 downwardly across the faceplate 64 during normal adjustment but is not suflicient to move theseelements when the mechanism is in the locked position. During normaloperation the force due to helical spring 188 is suflicient to balancethe force of spring 192 and also to move the chuck and the cam platesupward across the face of the face plate 64, as hereinbefore described.Thus, springs 188 and 192 protect the mechanism from damage which mightresult from attempts to force the mechanism beyond, for example, the A;lateral displacement for which the cam surface means of the illustratedform of invention are designed.

Referring to FIGS. 1, 2 and 4, angle plate 152 pivotally mounts on block206 a second cam lever plate 208 which is displaced 90 from cam leverplate 160. Cam lever plate 208, like cam lever plate 160, includes ahand operated cam lever plate adjusting handle 210 including an overloadspring assembly 212 which functions in the manner described withreference to the hand knob control assembly 174 described with referenceto FIG. 3 of the drawings. The reverse direction of movement of the camlever plate 208 is brought about by the return spring assembly generallydesignated 214 which is structurally and functionally the same as thereturn spring assembly described With reference to FIG. 3 and will nottherefore be described in detail.

The forward end of the cam lever plate 208 carries a generally U-shapedbracket member 216 which supports on one leg thereof a cam followerassembly generally designated 218. The cam follower assembly 218includes a cam roll 220 which is received in groove 90 between camsurfaces 92 and 94 and has a diameter substantially equal to the closestspacing B between the peaks of cam surfaces 92 and 94 as illustrated inFIG. 7 of the drawings.

By manual adjustment of the cam lever plate 208 adjusting knob 210, thechuck 76 and the attached 0am plates 80 and 84 are moved inward andoutwardly in a direction 90 displaced from the movement of said camplates and chuck brought about by movement of the hand control knobassembly 174.

As hereinbefore set forth, the cam surfaces, employed in laterallyshifting the chuck reltaive to the axis of the spindle, are four innumber, non-circular, and are eccentric to the bore in their respectivecam plate.

Referring to FIGS. 8 and 9, the development of cam surfaces 92 and 94and 98 and 100 are illustrated. In the illustrated form of theinvention, each cam surface 92, 94, 98 and 100 comprises three arcs. Forexample, cam surface 94 comprises arcs A C and D having centers A, C,and D respectively as ilustrated in FIG. 8. It will be noted that arcsforming the cam surfaces may be blended as at B and D where the arcsintersect to provide a smoothly curved cam.

While specific forms of cam surfaces have been illustrated, it will beapparent to those skilled in the art that substantially any form ofeccentric cam surfaces could be employed in the device. Further, it willbe apparent to those skilled in the art that each of the four camsurfaces may be provided on a separate cam plate instead of combiningtwo cam surfaces, one internal and one external, on each cam platewhereby a single cam follower may be employed for a pair of cam surfacesas in illustrated form of the invention.

Operation In operation of the improved centering mechanism of thepresent invention, the material to be worked is mounted in the jaws ofthe chuck 76. The handle 34 is rotated in a direction to back the drawbar 2'6 from the draw bar nut 82 which, in turn, relieves the forceapplied, by the plural helical springs 44, to the draw bar nut 82 which,in turn, relieves the force applied by the nut against the face of thegroove 110 cut in the forward face of the cam plate 80. This, in turn,reduces the friction between the cam plate 80, the anti-twist ring 78and the forward face of the face plate 64 permitting limited lateralmotion between cam plate 80 and the laterally fixed chuck plate 64. Itwill be particularly noted that reducing the friction between the camplate 80, the anti-twist ring '78 and the front face of the face plate64 does not effect the drive from the spindle 16 to the chuck 76 as thisdrive is through the cooperation between the four slots 121, 123, 124,and 125 in the antitwist ring 78 and the two slide blocks 134, 136,secured to the face plate 64 and the two slide blocks 142 secured to theback face of cam plate 80. The spindle is then rotated and the operatorapplies, for example, a dial indicator or shadowgraph to the work andeither hand knob 176 at the top of the headstock or the knob assembly210 on the side of the headstock 14 is adjusted to bring the runout ofthe work to a minimum. Ideally, the remaining runout can be removed byrotation of the other of the hand knob; however, in actual practice ithas been found that several successive adjustments of both of the knobs176 and 210 are usually required as it is difficult to make a fineadjustment for one component of motion when the runout due to the othercomponent is large. It has been found, however, that an experiencedoperator can reduce the runout to less than $0001 inch in less than aminute and to less than 10.0002 inch in about three minutes. After theadjustment of the knobs 176 and 210 is complete and the runout of thework is at a minimum, with or without stopping the machine, the operatortightens the draw bar by means of the handle 34 to lock the mechanism inits centered position. The locking takes place by causing the draw bar26 to be screwed further into the draw bar nut 82, increasing the forceon the springs 44 and drawing the draw bar and its handle assembly 34inwardly which, in turn, increases the force applied by the draw bar nut82 against the face of the groove in the cam plate 80. This increasesthe frictional engagement between the rearward face of the cam plate 80and the face plate 64 through the anti-twist ring 78. In general, thedraw bar is never completely slackened off since the spring pressure isused to provide some radial friction while making radial adjustments sothat the chuck assembly remains in the position it was placed by thelast adjustment of the cam adjusting control member.

If the operator wishes to displace the work laterally by a known amount,the operator chucks the Work so that the desired displacement will betowards the peaks of the cam surfaces 92 and 94. The Work is thencentered as previously described and the lathe is stopped with thepeaks, point B, of the cam surfaces 92 and 94 in contact with their camroller 220. The dial indicator or shadowgraph is zeroed when it is incontact with the work and the side knob assembly 210 is then moved untilthe indicator device shows the desired lateral movement of the workpiece.

From the foregoing description, it will be seen that an improved centeradjusting device is provided that fully accomplishes the aims andobjects of the invention. It will be apparent to those skilled in theart that various modifications may be made in the form of the structuresdescribed with reference to the illustrated form of the inventionwithout departing from the scope of the appended claims.

We claim:

1. In a machine having a headstock, a spindle mounted for rotation insaid headstock and a Work holding member rotatable with said spindle; acenter adjusting device comprising means mounting the work holdingmember in driven relation to the spindle including a plurality ofmembers having cam surfaces mounted for rotation with the spindle anddisplaceable with respect to the axis of rotation of the spindle in anyselected radial direction, means securing the Work holding member tosaid members having cam surfaces, cam followers adjustably supported bythe headstock of the machine and upon adjustment thereof adapted tocontact the members having cam surfaces and selectively move saidmembers having cam surfaces radially of the axis of rotation of thespindle, and locking means securing said members having cam surfacesagainst radial movement relative to the axis of rotation of the spindle.

2. In a machine having a headstock, a spindle mounted for rotation insaid headstock and a Work holding member rotatable with said spindle; acenter adjusting device comprising means mounting the work holdingmember in driven relationship to the spindle including a plurality ofmembers having cam surfaces mounted for rotation with the spindle anddisplaceable with respect to the axis of rotation of the spindle in anyselected radial direction, means securing the Work holding member tosaid members having cam surfaces, cam followers adjustably supported bythe headstock of the machine and upon adjustment thereof adapted tocontact the members having cam surfaces and selectively move said memberhaving cam surfaces radially of the axis of rotation of the spindle andadjustable friction means securing said members having cam surfacesagainst radial movement relative to the axis of rotation of the spindle.

3. In a machine having a headstock, a spindle mounted for rotation insaid headstock and a work holding member rotatable with said spindle; acenter adjusting device comprising means mounting said work holdingmember in driven relationship to the spindle including a pair of plateshaving cam surfaces thereon mounted for rotation with the spindle anddisplaceable with respect to the axis of rotation of the spindle in anyselected radial direction, means securing the work holding member tosaid pair of members having cam surfaces, a pair of cam followersadjustably supported by the headstock of the machine and upon adjustmentthereof adapted to contact the members having cam surfaces andselectively move their respective member of said pair of members havingcam surfaces radially of the axis of rotation of the spindle, andlocking means securing said pair of members having cam surfaces againstradial movement relative to the axis of rotation of the spindle.

4. In a machine having a headstock, a spindle mounted for rotation insaid headstock and a work holding member rotatable with said spindle; acenter adjusting device comprising means mounting the work holdingmember in driven relationship to the spindle, including a pair ofmembers having cam surfaces mounted for rotation with the spindle anddisplaceable with respect to the axis of rotation of the spindle in anyselected radial direction, the cam surfaces of said pair of membersbeing positioned eccentric to the axis of rotation of the spindle, meanssecuring the work holding member to said pair of mem' bers having saidcam surfaces, a pair of cam followers adjustably supported by theheadstock of the machine and upon adjustment thereof adapted to contactthe members having cam surfaces and selectively move said pair ofmembers having cam surfaces radially of the axis of rotation of thespindle, and locking means securing said members having cam surfacesagainst radial movement relative to the axis of rotation of the spindle.

5. The invention defined in claim 4 wherein each of said members havepaired cam surfaces with opposed cam peaks and the peaks of one of themembers is displaced with respect to the peaks of the other of themembers.

6. The invention defined in claim 5 wherein said pair of cam followersare circumferentially displaced 90 and are selectively movable towardand away from the axis of rotation of the spindle.

7. The invention defined in claim 4 wherein each of said pair of membershas a pair of opposed cam surfaces with the surfaces thereof disposedgenerally eccentric to the axis of rotation of the spindle and each ofthe pair of cam surfaces of each of said pair of members is engageableby a cam lever.

8. In a machine having a headstock, a hollow spindle mounted forrotation in the headstock and a work holding member rotatable with saidspindle; a center adjusting device comprising means mounting the workholding member in driven relationship to the hollow spindle including aplurality of members having cam surfaces mounted for rotation with thehollow spindle and displaceable with respect to the axis of rotation ofthe hollow spindle in any selected radial direction, means securing thework holding member to said members having cam surfaces, cam followersadjustably supported by the headstock of the machine and upon adjustmentthereof adapted to contact the members having cam surfaces andselectively move said members having cam surfaces radially of the axisof rotation of the spindle, a draw bar extending through the opening inthe hollow spindle, a draw bar nut threadedly engaging one end of thedraw bar and adjustable into frictional engagement with one of saidmembers having cam surfaces upon relative rotation of the draw bar withrespect to the draw bar nut to secure the members having cam surfacesagainst radial movement realtive to the axis of rotation of the hollowspindle.

9. The invention defined in claim 8 including means cooperating with thehollow spindle and said members having cam surfaces and mounting saidmembers for rotation with the hollow spindle and for limited radialmovement relative to said hollow spindle.

References Cited in the file of this patent UNITED STATES PATENTS1,751,772 Travis Mar. 25, 1930 2,423,312 Hamberger July 1, 1947 FOREIGNPATENTS 696,962 Germany Oct, 3, 1940

